A 5' to 3' single strand Dnase activity associated with isolated Ku protein was described in the previous annual report. The activity was found in both native and recombinant preparation. However, subsequent additional purification steps separated the Dnase activity from the bulk Ku protein itself. This work is being done by a post-dcotoral fellow, Dr. Viktor Morozov, who now has a position in the Laboratory of Dr. Lawrence Grossman of the Johns Hopkins School of Hygiene. The project has been discontinued. However, the enzyme, which appears to have as affinitiy for Ku, has properties appropriate for a role in double strand break repair and should be studied in detail. Immunostaining with uniquely specific antibodies indicated main redistribution of both Ku subunit proteins in response to increasing cell density, removal of serum and/or Ca2+ from the medium, and other manipulations that tend to inhibit growth rate. This work, described in detail previously, has been published, and the project discontinued.